Compute upper bound owner, group, and other file masks with as fewpermissions as possible without denying any permissions that the NFSv4acl in a richacl grants.

This algorithm is used when a file inherits an acl at create time andwhen an acl is set via a mechanism that does not specify file modes(such as via nfsd). When user-space sets an acl, the file masks arepassed in as part of the xattr.

When setting a richacl, the file masks determine what the filepermission bits will be set to; see richacl_masks_to_mode().